The present invention relates generally to machine tools and, more particularly, to a new and improved tool assembly for threading a workpiece.
The art is replete with machine tools, such as lathes and the like, adapted to rotate a workpiece such as a bar, pipe, bolt or other structure having an interior surface, or an exterior surface, which is to be threaded or otherwise formed with a helical groove. In such machine tools, a tool bit insert having a cutting edge made of a hardened material (such as tungsten-carbide) is clamped to a relatively massive shank member which, in turn, is securely mounted to the machine. The workpiece (which is mounted to another portion of the machine for rotation relative the cutting edge) and the insert cutting edge are brought together so that as the workpiece is rotated, the cutting edge of the insert cuts the threads or grooves in the desired surface.
In typical threading tool arrangements, a single tool bit insert is clamped to a shank (such as a boring bar shank) and the workpiece is rotated past the cutting edge of the insert to form a helical groove in the workpiece and define the desired threading configuration. After an initial groove is cut, the tool bit is brought back to its initial starting point and the process is repeated except that the insert cutting edge is re-positioned slightly for cutting slightly deeper into the workpiece on the next pass. The tool bit then makes numerous (15 or more depending on the depth of the groove and the hardness of the workpiece) successively deeper passes until the thread-groove has been cut to the desired depth. Although this approach has provided adequate results, it does entail a tedious and time-consuming procedure, resulting in unnecessary expense due to the inordinate number of repetitions of the machining step.
In an effort to improve the threading operation, there have been attempts to make a tool bit insert having several cutting edges by grinding the edges onto a single insert blank. The cutting edges are spaced to follow each other in the resultant groove cut in the workpiece and, like the single insert arrangement, are passed repeatedly over the workpiece, each time cutting a little deeper into the workpiece. Although such multiple-cutting-edge insert arrangements provide better defined grooves than a single-edge insert arrangement, it is limited in that if one cutting edge is damaged, the entire insert must be replaced while the depth and spacing of resultant thread-grooves is also limited. Moreover, it still requires about the same number of passes as the single insert.
it is, therefore, an object of the present invention to provide a new and improved tool assembly for machine tools and the like. It is another object of the invention to provide a new and improved tool assembly for forming threads or similar continuous grooving on a workpiece.
It is also an object of the present invention to provide a new and improved tool assembly for forming thread or the like on a workpiece, which forms the desired groove pattern on the workpiece with fewer (at least 50% fewer) repetitions of the machining step as compared with a single cutting edge threading tool.
It is a further object of the present invention to provide a new and improved tool assembly for forming threads or the like on a workpiece, which enables easy interchange or replacement of any one cutting edge without requiring replacement of all edges.
It is yet another object of the present invention to provide a new and improved tool assembly for forming threads or the like on a workpiece, wherein each tool bit insert is urged into further engagement with the back-stop bearing surface of the shank while engaged in the machining operation.
It is also an object of the invention to provide a new and improved tool assembly for threading or the like, which enables variations in the depth of the resultant groove as well as in the spacing between adjacent grooves.
It is still another object of the invention to provide a new and improved tool assembly for threading or the like, which enables the use of multiple identical inserts while minimizing the time for and repetitions of the machining steps and which provides automatic indexability of the tool assembly.
Objects and advantages of the invention are set forth in part herein and in part will be appreciated herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the instrumentalities and combinations pointed out in the appended claims. Accordingly, the invention resides in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.